In low side hermetic compressors all or most of the shell is filled with gas at suction pressure. The suction gas returns to the compressor at a relatively low temperature and it is commonly used to cool the motor. Cooling the motor with the suction gas warms the suction gas and reduces its density, thereby resulting in less mass being compressed for the same compressor displacement.
U.S. Pat. No. 5,055,010 is directed to a suction baffle for a low side hermetic scroll compressor. The suction baffle is secured to the shell and includes a "generously sized dome" which is "substantially centered vertically and circumferentially on (the) inlet port". Suction gas entering the compressor will tend to impinge upon the suction baffle such that entrained oil and liquid refrigerant will tend to collect on the surface and drain downwardly. Suction gas entering the compressor is divided into two flow paths. The first path is downward and is also the path of the separated liquids. Flow from the first path will then flow over and cool the motor. The second path is axially upward along a much longer, confined flow path opening into the interior of the shell. The reference is silent as to the division of the flows by percentage and as to their exact paths and recombination. With the symmetrically located dome facing the inlet, it is equally likely to divert the flow downwardly as upwardly. With a relatively very short path into the shell in the region of the motor, it is likely that at least half of the flow will be diverted downwardly and will flow over and cool the motor.
Commonly assigned U.S. Pat. No. 5,240,391 diverts a small amount, e.g. 15%, of the suction gas over the motor to cool the motor. After flowing over and cooling the motor, the diverted suction gas is aspirated into the major flow and supplied to the inlet of the scrolls for compression.
Because motors are designed to run at an elevated temperature, it is only necessary to cool them to their desired operating temperature. Any benefits to the motor from additional cooling of the motor are outweighed by losses in efficiency due to the heating of the suction gas.